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Specifying hygienic motor solutions

28 May 2019

Brian Bannister offers advice about what to look for when specifying motors and drives for use in hygienic applications. 

Different factors may be taken into consideration when selecting motors and drives, depending upon whether the specifier is an OEM of machinery/plant equipment, or the user of manufactured solutions.

Typically, an OEM might focus on the best performing package at an acceptable price which satisfies size and weight constraints, fulfils delivery targets and ultimately promotes repeat business.
 
The end user will have similar requirements but may put a greater emphasis on energy efficiency, hygiene, reliability and life-cycle costs.

According to mandatory legislation, all new equipment and systems incorporating 3-phase motors of 0.75kW and above, must use either IE2 efficiency-rated motors with an inverter, or IE3 motors if powered directly from the mains. Additionally, to build in a degree of future proofing, there is also the option of installing either IE4, or even IE5 motors.

Stainless-steel motors are ideally suited to hygiene-sensitive applications. Currently, IE3 stainless-steel motors covering a wide power range are available, even up to 15kW, with a more limited offering of IE4 asynchronous motors now on the market.

Painted motors that can be employed for less hygiene-sensitive duties are now widely available as IE4 and IE5 units. Based upon permanent magnet technology, in addition to providing high efficiency, these motors frequently offer a reduction in both weight and frame size which can help to reduce space and mounting requirements. While these motors require an inverter, there is an alternative option whereby permanent magnet motors are supplied with a built-in inverter as an integrated package. Utilising this solution ensures maximum motor/drive compatibility for optimum efficiency.

The role of an inverter is not just to provide variable speed and soft start functions, it can also help maximise operating efficiency. That could be energy efficiency, process control, or both by maximising or minimising energy demand according to varying process requirements, through either automated or manual control.

The efficiency of many fans and pumps is now assessed as a complete unit, with a motor and, where employed, a variable speed drive included in the calculation. It is the total combined efficiency performance that determines the efficiency rating of a fan or pump. Consequently, the greater the energy efficiency of the motor, the easier it becomes to meet or exceed the required energy rating as defined by Extended Product Approach (EPA).

Hygiene
Historically, there have been a limited number of options regarding motors and gearboxes to satisfy the hygiene needs of the food industry.

Currently, solutions involving conventional finned motors include units painted with 2-pack epoxy compounds and/or shrouds. The 2-pack epoxy compound partially resolves the issue, but it is still vulnerable to flaking if the coating seal is broken. Shrouds, again, do provide a degree of protection but can hide issues arising from moist environments and air-borne product/contaminants. Neither option, however, overcomes the issue of entrapment areas, where material can potentially build-up, creating a contamination risk.

Another solution employed by some companies is the bagging of motors using plastic bags while machinery is hosed down. Although this might protect the motors from water ingress, there remains the issue of motors not being cleaned properly, rendering the procedure pointless.

Today, stainless steel options are available for both motors and gearboxes. Designed with the strict hygiene standards of the food industry in mind, they are smooth bodied and IP69K (IP66) rated, making them hose-down tolerant helping speed up effective cleaning operations. To complete the offering, there are now also IP66 rated stainless steel inverters enabling total systems to be installed in wet, wash-down areas.

Hose-down tolerant (IP69K/IP66) stainless-steel motors were important for a potato processing plant where waste material and water from a produce transfer pump fall directly onto the pump’s drive motor. The company found that standard, finned motors; although brushed down frequently; became corroded and had crevices that could trap product waste. A replacement stainless, smooth-bodied motors, however, can be hosed down quickly and there is nowhere for material to become trapped to potentially cause hygiene issues.

Customisation
To provide solutions for difficult, non-standard applications, customised stainless motors have been supplied with features such as compact non-contact shaft sealing systems; integrated and encapsulated cable/terminal boxes; stainless steel brakes, encoders, customer-specified shafts and flanges, and to complete the system, IP66 inverters.

In one application a non-contact sealing system was required where the motor is mounted with the shaft in a vertical position and there is a constant water/product waste presence. Standard, painted motors used previously in this mounting position would only last a few over more than six months. If new, non-contact seals are used, this would be extended even further.

Motor terminal boxes are usually the most vulnerable element of the complete unit, providing the easiest access point for moisture. To overcome this issue for wash-down locations some stainless motors are offered with welded, fully-integrated terminal boxes with an option for encapsulated connection terminals. As an integral part of the motor body housing encapsulated electrical terminals the terminal box protects the electrical connections effectively, even where hose-down cleaning is employed.

Installation and maintenance
To ensure maximum operating efficiency and longevity, all motors should be installed and maintained correctly according to manufacturers’ recommended installation procedures.

Simple things such as ensuring external dimensions of cables and cable glands are correctly sized and terminal box lids are closed properly, to ensure moisture is effectively excluded, are essential to help promote effective motor performance and reliability. Furthermore, cables must be looped correctly to prevent moisture ingress into terminal boxes through distorted glands. To observe the correct method of installation, power supply cables should loop below the entry gland to encourage any liquid they might carry to flow away from that potential entry point.

It is also important to note the position and angle of mounting of motors, as additional measures may need to be employed to ensure correct installation. Unused glands, for example, should be positioned and effectively closed to avoid the risk of moisture ingress. Regarding the angle of motor installation, if installed vertically for example, the shaft must have effective sealing or protection to prevent moisture penetration causing motor failure.

Even when motors are installed correctly they should be inspected at planned intervals components such as seals, glands and bearings are all prone to wear or deterioration.

This posed a problem for an Australian cheese manufacturer who made the decision to replace its conventional AC and DC motors with stainless motors to overcome the problem of salt-initiated corrosion of motor bodies and bearings, despite protection by a shroud. According to the manufacturer, the installation of stainless motors has eliminated all corrosion and maintenance and the stainless motors have been running effectively for over two years.

For many it is the economics of installing stainless motors is just as important as the enhanced hygiene. For one blue-chip bakery this was definitely the case. Reduced downtime, simplified cleaning operations and the significantly increased lifespan of stainless motors resulted in a payback in under six months. Stainless motors were first installed on egg glazing lines, where motors and mountings were removed and dismantled every night for cleaning by hand. Since installation,  the stainless motor allows the motor assembly to be simply steam cleaned as a complete unit, speeding up the daily cleaning operation.

The elimination of motor failures has saved another food processor thousands of pounds in maintenance costs since the installation of stainless motors. The breakfast cereal manufacturer initially installed two stainless-steel motors on extruders on different production lines as part of a reliability improvement programme. They needed to operate in a hot and steamy environment and, because they became coated in product material, were subjected to high pressure hose cleaning. A trial programme showed standard motors lasted 30-40 days, modified standard motors ran for 114 days, while the stainless motors were still working after more than a year.

Brian Bannister is a motor specialist at Lafert Electric Motors.


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